new to 3.2, VBO problems

OpenGL OpenGL: Basic Coding
1

Ok I recently came back to some OpenGL development, but my experience dates back to 1999 and I mostly used immediate mode stuff (glBegin, glEnd, etc).

So I started reading into OpenGL 3.2 + GLSL 1.5 and my assumption is that everthing now is done with VBOs and Vertex/Geometry/Fragment shaders … am I right?

I succesfully initiated a “3.2.9704 Forward-Compatible Context” on Linux (Ubuntu 9.10) with a HD 4850.

So far I got shaders loaded and executed allright, and I can draw a simple quad using a VBO and glDrawElements() with an indices array.
Is this how all drawing is supposed to happen now?

Now I met a problem in this early stage:
I am using a second VBO with vertex color values (3 floats each) and the vertex shader inputs the color and transfers it to the fragment shader.
The first 2 vertices are drawn with the correct color, but then color values don’t match the supplied array.

What am I doing wrong here?

(vertex, fragment shader, relevant C++ code)


#version 150

in vec4 vertex;
in vec3 col;

out vec3 v_col;

void main(void) {
	v_col = col;
	gl_Position = vertex;
}



#version 150

in vec3 v_col;

out vec4 fragColor;

void main(void) {
	fragColor = vec4(v_col, 1.0);
}



void createBuffers(GLuint program) {
	// generate vertex data
	GLfloat data[] = {
			-1.0,  0.0, 0.0,
			 0.0,  1.0, 0.0,
			 1.0,  0.0, 0.0,
			 0.0, -1.0, 0.0
	};

	GLfloat color[] = {
			 1.0, 0.0, 0.0,
			 0.0, 1.0, 0,0,
			 0.0, 0.0, 1.0,
			 1.0, 1.0, 1.0
	};

	// VertexArrayObject is needed - ToDo: lookup what a VAO is
	GLuint vao;
	glGenVertexArrays(1, &vao);
	glBindVertexArray(vao);

	// vertex data
	glGenBuffers(1, &buffer_data);
	glBindBuffer(GL_ARRAY_BUFFER, buffer_data);
	glBufferData(GL_ARRAY_BUFFER, sizeof(data), data, GL_STATIC_DRAW);
	// map input attribute: vertex
	GLuint attr_vertex = glGetAttribLocation(program, "vertex");
	glVertexAttribPointer(attr_vertex, 3, GL_FLOAT, GL_FALSE, 0, 0);
	glEnableVertexAttribArray(attr_vertex);

	// color data
	glGenBuffers(1, & buffer_color);
	glBindBuffer(GL_ARRAY_BUFFER, buffer_color);
	glBufferData(GL_ARRAY_BUFFER, sizeof(color), color, GL_STATIC_DRAW);
	// map input attribute: col
	GLuint attr_color = glGetAttribLocation(program, "col");
	glVertexAttribPointer(attr_color, 3, GL_FLOAT, GL_FALSE, 0, 0);
	glEnableVertexAttribArray(attr_color);
}

void render() {
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glBindBuffer(GL_ARRAY_BUFFER, buffer_data);
	glBindBuffer(GL_ARRAY_BUFFER, buffer_color);

	GLuint indices[] = {0, 1, 2, 2, 3, 0};
	glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, indices);


	glutSwapBuffers();
	glFlush();
}